Carrier AquaEdge 19XR Series Start-up, Operation And Maintenance Instructions Manual

Also see for AquaEdge 19XR series: Installation instructions Start-up, operation and maintenance instructions

Contents

11Fig. 7 — Refrigeration Cycle — 19XR(V) Two-Stage CompressorMOTOR AND OIL COOLING CYCLEThe motor and the lubricating oil are cooled by liquid refrigeranttaken from the bottom of the condenser vessel (Fig. 8 and 9). Re-frigerant flow is maintained by the pressure differential that ex-ists due to compressor operation. After the refrigerant flows pastan isolation valve, an in-line filter, and a sight glass/moisture in-dicator, the flow is split between the motor cooling and oil cool-ing systems.Flow to the motor cooling system passes through an orifice andinto the motor. Once past the orifice, the refrigerant is directedover the motor by spray nozzles. The refrigerant collects in thebottom of the motor casing and is then drained back into the cool-er through the motor refrigerant drain line. An orifice (in the motorshell) maintains a higher pressure in the motor shell than in thecooler. The motor is protected by a temperature sensor embeddedin the stator windings. An increase in motor winding temperaturepast the motor override set point overrides the temperature capaci-ty control to hold, and if the motor temperature rises 10F (5.5C)above this set point, the controls close the inlet guide vanes. If thetemperature rises above safety limit, the compressor shuts down.Refrigerant that flows to the oil cooling system is regulated by ex-pansion valves. The expansion valves regulate flow into the oil/re-frigerant plate and frame-type heat exchanger (the oil cooler inFig. 8), and control oil temperature to the bearings. The refrigerantleaving the oil cooler heat exchanger returns to the chiller cooler.VFD Cooling CycleThe unit-mounted variable frequency drive (VFD) is cooled in amanner similar to the motor and lubricating oil cooling cycle. Ifequipped with a unit-mounted VFD, the refrigerant line that feedsthe motor cooling and oil cooler also feeds the heat exchanger onthe unit-mounted VFD. Refrigerant is metered through an orificeas refrigerant is leaving the VFD heat exchanger. The refrigerantleaving the heat exchanger returns to the cooler.CAUTIONTo avoid adverse effects on chiller operation, considerationmust be made to condenser water temperature control. Forsteady state operation, the minimum operating refrigerantpressure differential between cooler and condenser is approxi-mately 20 psi (138 kPa) with a maximum evaporator refriger-ant temperature of 65°F (18°C). Consult Chiller Builder for re-quired steady state operational limits. Inverted start conditionsare acceptable for short durations of time, but for periods ex-ceeding 5 minutes, a special control solution strategy shouldbe used to allow the chiller to establish a minimum refrigerantpressure differential, and thereby adequate equipment cooling.